Conventionally, in electric welding and other disconnectable uses of heavy plug-in extension cables for transmitting high amperage electrical currents, a cylindrical conductive female connector socket and a male twist lock plug-in are generally used.
A standard heavy duty plug-in socket unit for handling high amperage electrical currents has a molded insulating body having a coarsely threaded shank provided with external chordal faces and indexing tabs thereon non-rotatably engaging a front panel member having correspondingly shaped openings. A thick external cylindrical flange is provided around the socket opening at one end and engages the outside face of the panel from which it extends a substantial distance beyond the panel for strength and engagement against the outside face for securement by a lock washer threaded on the shank of the plug to clamp the flange and socket member tightly in place.
However, repeatedly used conventionally mounted plug-in sockets work loose and cannot be safely retightened without opening a cabinet where the heavy bus bars are located that carry different electric current potentials which are dangerous to personnel. Time and effort is required for safety sake to remedy such loosenings, and procrastination occurs.
More particularly, the cylindrical flange around the plug-in socket is subjected to the lateral and axial back and forth effort of a plugged-in flexible cable connector as a compounded loosening universal lever-like action along with the pull and twist movement of the plug in which the primary plug-in effort on the plug is expended inwardly on the socket in a direction that tends to relieve axial tension on the lock washer. This is followed by a rotational movement of the plug that urges the lock washer to rotate in a clockwise direction. Then when removing the plug, the lock washer is pulled tighter against the back side of the panel and any rotational component of movement is in the counter-clockwise direction of unthreading the tightly drawn lock washer, ever so slightly, each time.
Furthermore, the work strain upon a twist lock, plugged-in flexible cable, in use, also provides leverages against the exposed flange thickness of the plug which, over a period of time, gradually accelerates a loosening of the lock washer on the threaded shank which also in turn loosens progressively more rapidly. Also, although the back and forth use movement of the heavy plugged-in cables may loosen some of the most used sockets in a multi-outlet cabinet there may be no critical progressively loosening of other sockets receiving a lesser use of plug-in cables. However, a shut off and repair of the whole panel for the sake of safety to prevent possible shorts with bus bars is required to tighten any loose sockets even though only a few of several might be involved.
The use of a lock washer and a nut merely compounds the differential action among the parts if the bus bar connections also happen to serve as pivot points.